Silver particles with various shapes are used to build conductive elements in plasma display panels, multi layer ceramic capacitors, solar cells, printed circuit boards and many other thick film components incorporated in most electronics surrounding us. The technological progress in these applications depends increasingly on the ability to control the size, shape, and internal structure of the particles. Highly dispersed uniform spherical silver particles are particularly important for the electronic industry, as they provide very distinct advantages. In the manufacturing of plasma display panels silver spheres with a smooth surface allow a better photolithographic patterning. The superior packing of such particles favors the formation of compact ‘green’ structures that yield continuous conductive sintered layers. Most silver powders presently used in electronics are generated by processes using high molecular weight polymers as dispersants and contain residual organics which can interfere with their sintering.
Fine silver particles have been prepared by various methods including the reduction of silver salts in solutions or reverse micelles systems, photoreduction, and thermolysis. The precipitation in homogeneous solutions is by far the most versatile approach due to the broad range of solvents available and the large variety of reductants, dispersants, and complexing agents. Although there are a few methods capable of generating large silver spheres in the absence of dispersants but they use low metal concentration and undesirable chemicals. Therefore, the present inventors desired to create an improved method of formation of well dispersed, uniform large spherical silver particles, without polymers as protective colloids.
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